In grate fired boilers or like devices, fuel (solids) to be burned is fed onto a grate, at times along with combustion aids such as gas or oil. Herein the term “solids fuel” is at times referred to as “fuel”. The heat from the burning fuel is commonly used to generate steam. In the prior art, the rate of feeding of the fuel onto the grate has been manually controlled by an operator who uses visual observations, including use of cameras, and/or pyrometers as the tools for making judgment calls. It will be recognized that each of these methods of monitoring the progression of the burning of the fuel and the rate on incoming fuel to feed the combustion do not have the ability to provide a clear indication of the amount of material residing on the grate at any given time or over a period of time. Grates in boilers may comprise a continuous grate which is moved forwardly through the burner section of the boiler wherein the fuel is consumed and ash is generated. In this type boiler, the ash is carried out of the burner section and dumped into an ash bin by the moving grate. In other boilers, the grate may be mounted in place, but is vibrated to enhance combustion and to separate ash which falls through the grate into an ash bin. The present invention may be employed with either type grate, but is especially useful when employed with a forwardly moving grate.
Burning of fuel on a grate fired boiler is often limited due to the risk of excessive piling on of the fuel on the grate with an accompanying “over heating” or “under heating” of the water associated with the boiler, resulting in excessive production or insufficient production of steam output from the boiler or decrease in the efficiency of the burning process. This leads to lost opportunities to burn low cost solids fuels rather than higher cost oil or gas, for example. Oil or gas combustion enhancers can be used to relatively rapidly alter the heat generated in the burner section of the boiler, hence are convenient to use, but costly as concerns operational expense for the boiler. Since operator concern relating to excessive amounts of feed (and/or ash) material on the grate can limit the amount of material burned over a given time period and/or substantially decrease the permissible maximization of the feed of the fuel to the burner, a direct measurement of the weight of feed (and/or ash) on the grate is desirable so that lost opportunities to burn solids fuel can be eliminated and optimization of the burning process may be realized. It is projected that as much as a 10–20% incremental increase in the amount of solids fuel burned over a given period of time may be achieved if the fuel feed rate could be optimized.